1. Technical Field
The present invention relates to a rotation angle detection apparatus, and a control method and control program of the rotation angle detection apparatus, and particularly to a rotation angle detection apparatus, and a control method and control program of the rotation angle detection apparatus, for detecting a rotation angle (a rotation angle within a two-dimensional image plane) of an object such as a person's facial image in a detection subject image.
2. Related Art
To date, a detection of a person's face has been carried out assuming a variety of applications, such as an identification photograph or a management of entering and leaving a room by means of a facial recognition.
For example, with the identification photograph, a position in the photograph, a size, a direction of a face, and the like, are stringently fixed.
Also, although a variety of facial detection and facial recognition technologies are known, they are carried out under a precondition that the face is in an upright condition.
As such, it can be easily understood that detecting the direction of the face, and correcting it perpendicularly, has a considerable effect on a widening of the applications, and an accuracy of the facial detection and facial recognition.
As this kind of technology, a technology which, calculating reference parameters from a center of a flesh color area and feature points of the face, detects a rotation angle (an inclination) on an image plane of the face, is disclosed in Japanese Patent No. 3,454,726.
However, depending on differences in skin color caused by differences in race, and lighting conditions, a range of apparent colors changes considerably. Also, depending on an orientation of the face too, the range of the apparent colors has changed considerably.
As a result, with the heretofore described related art, there has been a problem in that it is not always possible to detect an accurate rotation angle of the object.